nLab precision experiment

Idea

In particle physics experiments, there tends to be a dichotomy between direct detection at high energy and indirect detection via high precision.

Traditionally, direct high energy experiments have been dominating the field since the discovery of heavy quarks in large accelerator experiments, culminating in the discovery of the Higgs boson at the LHC experiment. Here the particle being detected is an actual decay product of the scattering process.

But heavy fundamental particles, whose mass may be beyond that of direct reaction products obtained in a given accelerator experiment, may still manifest themselves indirectly, as virtual particles contributing to loop corrections of the scattering amplitudes of all lighter particles to which they couple. Therefore, sufficiently precise measurement of light particle decays at low energy may still reveal the presence and properties of virtual particles at (much) higher energy.

Discerning the small statistical effects expected in precision experiments requires access to a large amount of experimental data, hence to a high intensity of particle scattering processes, whence the community refers to precision experiments as probing “the intensity frontier” of particle physics (see the references below). This is in contrast to direct detection experiment which can do with less data as long as it concerns high energy scattering processes, whence direct detection experiments are said to be probing “the energy frontier” of particle physics.

An example for a potential effect seen in precision experiments are the flavour anomalies in B-meson decays at various experiments, including the LHCb experiment, Belle experiment and BaBar experiment.

Since, at the same time, the LHC experiment has not made any further direct detection, beyond the Higgs boson, it has been argued that indirect precision experiments will or should gain in importance in the future of particle physics.

References

General:

• Brambilla et al., Section 5 of: QCD and strongly coupled gauge theories - challenges and perspectives, Eur Phys J C Part Fields. 2014; 74(10): 2981 (arXiv:1404.3723, doi:10.1140/epjc/s10052-014-2981-5)

With focus on Higgs field-interactions:

• Gudrun Heinrich, Collider Physics at the Precision Frontier, Physics Reports, Volume 922, 2021, Pages 1-69 (arXiv:2009.00516)

• Sven Heinemeyer, Stanislaw Jadach, Jürgen Reuter, Theory requirements for SM Higgs and EW precision physics at the FCC-ee (arXiv:2106.11802)

In view of potential leptoquarks:

• I. Doršner, S. Fajfer, A. Greljo, J. F. Kamenik, N. Košnik, Physics of leptoquarks in precision experiments and at particle colliders, Physics Reports Volume 641, 17 June 2016, Pages 1-68 (arXiv:1603.04993)

In view of flavour anomalies:

• Rafael Aoude, Tobias Hurth, Sophie Renner, William Shepherd, The impact of flavour data on global fits of the MFV SMEFT (arXiv:2003.05432)

On the “intensity frontier”-terminology:

• Elizabeth Clements, New tools forge new frontiers, Symmetry Magazine, Aug. 2008 (pdf)

• J. L. Hewett et al. Planning the Future of U.S. Particle Physics (Snowmass 2013): Chapter 2: Intensity Frontier (arXiv:1401.6077)

and in regards to the Belle II experiment:

• Snowmass White Paper: Belle II physics reach and plans for the next decade and beyond [arXiv:2207.06307]

  Belle II is an experiment operating at the intensity frontier.

With emphasis on precision QCD-predictions:

• Thomas Gehrmann, Bogdan Malaescu, Precision QCD Physics at the LHC (arXiv:2111.02319)

• Francesco Giuli, High-precision QCD physics at FCC-ee [arXiv:2208.09621]